Bhotekosi/Rasuwa Flash Flood Initial Assessment

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Post Flood

Affected Settlements

Debris Flow Source Area

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Drag the vertical handle on the map to compare the basemap (left of the handle) with the post‑flood NDWI overlay (right of the handle). Works while panning and zooming.

Analysis Summary

On 26 August 2026, the disaster began with a glacier related slope failure that generated an ice and catastrophic debris flow, and the flood was likely triggered from the border with China. The slope failure generated energy equivalent to a M5.2 earthquake (USGS). This debris flow and flooding travelled nearly 100 km and impacted populated areas downstream along the Rasuwagadhi border post between China and Nepal. Based on this preliminary imagery analysis, more than 6,000 buildings and infrastructure have likely been affected and destroyed, including vital highways: Prithvi Highway, Pasang Lhamu Highway, Trishuli–Mailung–Syabrubesi Road, and 11 hydropower projects.

Along with the flood damage, I also looked at temperature and warm-period trends in the area where the flood started, using ERA5 Land data (9km) from 2016 to 2026. This showed another important sign. There is no clear year-by-year rise in temperature in that area, at least from this analysis. But in recent years, especially after 2020, warm periods (above 8°C) have been lasting longer. In 2024, there was a 24-day warm spell from 13 July to 5 August, the longest in this period. 2025 and 2026 also had relatively long warm spells (11 days in August 2026 alone, with a mean of 8.30°C). Whether these longer warm periods played a role in this disaster is something future studies will need to figure out.

Note: This is a preliminary analysis using Sentinel-2 imagery (10 m) and the water index NDWI, which has not been validated in the field

Basemap

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